This is the only and real fix to this problem.
Problem: Receiving error code A.B.C.D.E.F.-.H.I.J.K.-.-.N.-.-.-.-.-.-.U. when trying to login to online service.
Solution: Simple! Wait in start screen and be patient.
Really, all you have to do is wait until the game fetches latest updates from the COD servers. Don’t press X until, the game is ready to start. That’s the case when the version number in the upper right corner changed from XY.0.0.0.0 to somthing like XY.XY.XY.XY.0
The client (your game) will download updated game files from the COD-servers.
This may take a while (up to 5 minutes ore more).
After version number stopped changing press X and the game should start as normal.
If this won’t work at first time, reboot your PS4, make sure your internet connection is working, check the game for updates and start up again.
Further explanations: BO3 version number
The first two digits represent the mayor updates. That’s the updates you receive from the PSN and which are located on your HDD and loaded at startup. At the moment its 65.
The other following digits seems to represent the server-sided version and has to be checked every time you start the game resp. login to the COD-servers.
If the login servers are busy, because rush-hour and big updates, fetching updated files on login can take a while.